1. Field of the Invention
The present invention relates in general to a washing machine and a control method thereof, and more particularly, to a washing machine and a control method thereof, which are improved in circulation mechanism of washing water.
2. Description of the Related Art
Recently, various washing machines have spread to a household according to the developments of washing technology such as a washing by means of air bubbles, a washing by striking the laundry with washing water, etc. Thus, the time and labor required for washing is greatly saved.
Nevertheless, there is a shortcoming that dirt is not completely removed in the case of washing white clothes. Moreover, in the case of washing underwears or baby clothes, a user wants not only a washing but also a bleaching and sterilization. Also, it is necessary to boil underwears contacting with a human body, because of an environmental contamination.
As shown in FIG. 8, a conventional washing machine having a boiling function is comprised of a cabinet 110 having a top opening 112 through which the laundry and a detergent are received; and a cover 114 opening and closing the top opening 112.
The cover 114 is comprised of an inside cover 116 for covering a heating tank 140 and an outside cover 122 above the inside cover 116.
Outside the cabinet 110 are installed a selection button 136 allowing a user to control to machine and a power controller 132 controlling a heater 150 according to a temperature signal from a temperature sensor 152.
Inside the cabinet 110 is provided the heating tank 140, being separated from the cabinet 110 by a predetermined distance, accommodating the washing and the detergent.
In the lower part of the heating tank 140 is installed the heater 150 boiling the washing by heating washing water. One side of the heater 150 is provided the temperature sensor 152 sensing a washing water temperature in the heating tank 140 heated by the heater 150. Above the heater 150 is horizontally provided a blocking plate 154 preventing the washing in the heating tank 140 from contacting with the heater 150. The blocking plate 154 has a plurality of holes 156 through which washing water flows.
With this configuration, in the conventional washing machine having the boiling function, a user puts washing water in the heating tank 140 with the washing and the detergent, and closes the inside and outside covers 116 and 122. Thereafter, the user sets up a washing time and operates the heater 150 to heat the washing water until a temperature of the washing water rises to a predetermined temperature. If the temperature of the washing water sensed by the temperature sensor 152 rises to the predetermined temperature, the heater 150 stops operating. Contrarily, if the temperature of the washing water in the heating tank 140 is lower than the predetermined temperature, the heater 150 is continuously operated to make the washing water rise to the predetermined temperature during the set up time in the power controller 132.
If the above operations continue by the set up time, then the heater 150 stops operating, and the user picks out the washing from the heating tank 140 and washes it a separate washing machine or a hand washing.
However, in the conventional washing machine having the boiling function, while the lower part of the heating tank is heated to a relatively high temperature, the upper part thereof is is heated to a relatively low temperature because the washing interrupts heat transfer.
That is, even if the lower part temperature of the heating tank rises to the predetermined temperature, the upper part does not. Therefore, the temperature of the washing in the upper part of the heating tank does not reach the predetermined temperature. Consequently, the conventional boiling washing machine cannot boil the washing evenly, thereby lowering the efficiency of sterilization, bleaching and washing.
Moreover, the washing efficiency of the washing floating in washing water becomes sharply lower than to the washing efficiency of the washing soaked therein. If the temperature of washing water rises, the part of the washing contacting with air is oxidized, and therefore it may be damaged.
In addition, in the conventional boiling washing machine boiling the washing is restricted according to a material of the washing, and it is difficult to boil the washing with low temperature in the case of the washing which is not allowed to wash with a high temperature, thereby lowering the washing efficiency.
Further, since there is no drain system in the heating tank, it is required to wait until washing water becomes cool, in order that a user pumps out hot washing water with user's own hands.